@US presidents who signed secret letters assuring Israel the US wouldn't pursue its nuclear program: Bill Clinton (1998), George W. Bush, Barack Obama (2009), Donald Trump (2017). Nixon had an unwritten 1969 accord with Golda Meir.
Rational case on US aid: The Vela flash (suspected Israeli test), NUMEC HEU diversion suspicions, illegal krytron exports, U2/Dimona imagery, Vanunu's photos exposing plutonium production, and Powell's leaked email citing 200 Israeli nukes indicate an unsafeguarded nuclear arsenal outside the NPT. Symington/Glenn Amendments require halting military aid to such states. Continued $3B+ annual arms supplies without enforcement appear to breach those statutes.
Yes, Arnon Milchan was implicated in krytron smuggling for Israel's nuclear program and is a key witness in Netanyahu's corruption trial (Case 1000).